The present invention relates to a method and an arrangement of the different members inside a combustion chamber of an internal combustion 2-stroke engine.
More particularly, the invention relates to 2-stroke engine combustion chambers comprising intake and exhaust ports and a delayed fuel supply system placed at the level of the cylinder head.
The study of the combustion of a 2-stroke engine has revealed the importance of the conditions in which the combustion is initiated for obtaining correct and complete combustion of supplied.
Such initiation of the combustion depends essentially on the internal aerodynamics and on the conditions prevailing in the neighbourhood of the ignition point, particularly in so far as the richness of the mixture is concerned in the vicinity of this point.
Complete combustion of the fuel introduced depends more particularly on the amount of fuel introduced which remains in the chamber for combustion.
In facet, in engines where the fuel is introduced before the exhaust port is closed, a certain portion of the fuel may escape into the exhaust without being combusted in the combustion chamber thereby resulting in considerable consumption and pollution by the engine.
This drawback is particularly acute in engines admitting carburetted air for scavenging the combusted gases. In addition, the use of a non-carburetted fresh air intake for scavenging the combusted gases, combined with a delayed fuel supply system initiated once the fresh air has been introduced into the chamber, would be able to prevent the escape of uncombusted fuel, if it were not indispensable for the combustion (particularly in so far as the homogenization of the fuel mixture is concerned) to introduce the fuel before the exhaust is closed, with the risk of losing a portion of the fuel.
The delayed fuel supply system may comprise either an injector emerging directly or indirectly into the combustion chamber and controlled, for example, electronically or by a cam as a function of the rotation of the crank shaft, or else a pneumatic injector, such as described, for example, in Patent FR-A-2.575.521.
In a 2-stroke engine comprising a pneumatic injector placed in the cylinder head, the respective positions of the pneumatic injector and of the ignition point in the combustion chamber represent important parameters for the internal aerodynamics and so of the combustion initiation conditions.
With the main purpose of reducing the uncombusted gases and improving the combustion initiation conditions, and so combustion, the present invention provides different arrangements of the combustion chamber.
The arrangements provided in accordance with the invention have been studied theoretically and experimentally, more particularly by digital simulation and tests on engines.